Circuit arrangements for the indication of lamp failure

ABSTRACT

An electric warning system for a pair of parallel-connected lamps includes a warning lamp in series with a thyristor across the system input terminals. A resistor is connected in a first series circuit with the lamps and in a second series circuit with a transistor and a capacitor across the input terminals. The transistor is biased to cut-off by means of second and third resistors in series across the input terminals. The circuit components are arranged so that failure of either lamp turns the transistor &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39; to charge the capacitor. The capacitor voltage is coupled to the thyristor control electrode to trigger the thyristor &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39; when a given capacitor voltage level is achieved. A switch is provided in the circuit so as to remove the input voltage from all of the circuit components except the thyristor and the warning lamp.

United States Patent Rumpf 4s May2, 1972 UNITED STATES PATENTS 3,271,7369/1966 Brown e: al..... ..340/25l 2/1969 Carp et al. ..340/25l CIRCUITARRANGEMENTS FOR THE INDICATION 0F LAMP FAILURE Paul Rumpt, Kew East,Australia Inventor:

Assignee: U.S. Philips Corporation, New York, NY. Filed: A r. 7,1970

Appl.No.: 26,205

Foreign Application Priority Data Australia ..53 I 56 Apr. 8, 1969 U.S.Cl. ...340/52 R, 180/103, 340/251 Int. Cl .3601 1/00 Field of Search..340/52 F, 251, 80, 79, 74,

References Cited 3,514,751 5/ 1970 Pascente....; ..340/52 PrimaryExaminer-John W. Caldwell Assistant Examiner-Glen R. Swann, 111Attorney-Frank R. Trifari [57] ABSTRACT An electric warning system for apair of parallel-connected lamps includes a warning lamp in series witha thyristor across the system input terminals. A resistor is connectedin a first series circuit with the lamps and in a second series circuitwith a 1 1 Claims, 3 Drawing Figures PATENT'EDMM 2 m2 Fig.3

INVENTOR.

PAUL RUMPF M 8% AGENT CIRCUIT ARRANGEMENTS FOR "ms INDICATION or LAMP FILURE BACKGROUND OF THE INVENTION This invention relates to a circuitarrangement for the direct current supply of a first lamp, particularlya motorcar lamp, and for signaling the failure of said first lamp withthe aid of an auxiliary lamp. In a circuit of this type, an inputterminal of the circuit arrangement is connected to one end of adiagonal of an electric bridge and the other input terminal is connectedto the other end of said bridge diagonal, a resistor being provided inthree limbs of the bridge and the fourth limb of the bridge comprisingat least the first lamp. The ends of the other bridge diagonal areconnected to a main electrode-respectively the base-of a transistor, theother main electrode of which is connected through a subsequent circuitelement to the negative input terminal.

A circuit arrangement of the kind described above is shown, for example,in British Pat. No. 947,491 (see, for example, FIG. 1 of said patentspecification). A drawback of this known circuit arrangement is thatwhen two parallel-arranged main resistor which is series-arranged withthese lamps is reduced, and the resultant emitter-base voltage of thetransistor is sufficient to make this transistor conduct, the saidcapacitor is charged through this transistor. Namely the transistorcurrent .by which this is effected need only be very low for thiscurrent need not flow through the warning lamp. The result thereof isthat this auxiliary current does not bring about a great variation inthe potential across the resistor which is series-arranged with the mainlamp so that the transistor remains conducting for some time. If thecapacitor has obtained such a charge that the trigger voltage of thethyristor has been reached the connection of the input terminals throughthe lamps instead of one main lamp are used, the failure of one of thesemain lamps does not lead to satisfactory signaling by the auxiliarywarning lamp. In fact, one starts from two parallelarranged main lampsand if upon failure of one of the lamps the base of the said transistorwould receive a voltage such that this transistor becomes conducting,the auxiliary lamp in the known circuit starts to draw current so thatthe voltage of the emitter of the relevant transistor also becomes morenegative which in turn would lead to the transistor becomingnonconducting. A satisfactory lighting up of the warning lamp and hencea satisfactory signaling of the fault (the failure of one of the mainlamps) is thus not achieved with this arrangement.

Groups of two parallel-arranged lamps are frequently used, particularlyfor motorcar lighting. Consider, for example, the two stop lights, orthe two headlights on the front side of the car, or the blinkers of thevehicle. In the interest of road safety, it is of paramount importancethat a motorcar driver know whether all of these lamps systems arefunctioning in the correct manner and that he receive a timely signalwhen one of these lamps has failed. This is of course of paramountimportance in so far as the stop lights are concerned.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide a simple circuit for the case of two or moreparallel-arranged lamps which circuit signals the failure of one ofthese lamps.

A circuit arrangement according to the invention for the direct currentsupply of a first lamp, particularly a motorcar lamp, and for signallingthe failure of said first lamp with the aid of an auxiliary lamp, aninput terminal of the circuit ar-- rangement being connected to one endof a diagonal of an electric bridge and the other input terminal beingconnected to the other end of said bridge diagonal, a resistor beingprovided in three limbs of the bridge and the fourth limb of the bridgecomprising at least the first lamp, the ends of the other bridgediagonal being connected to a main electrode-respectively the base of atransistor, the other main electrode of which is connected through asubsequent circuit element to the negative input terminal ischaracterized in that a second lamp is arranged parallel to the firstlamp and that the subsequent circuit element which is connected to thetransistor includes at least a capacitor, a junction between thistransistor and the capacitor being connected to the control electrode ofa thyristor, the input terminals of the circuit arrangement being alsoconnected by means of a series arrangement of the auxiliary lamp and thethyristor, all this in such a manner that in the presence of a voltageacross the input terminals, but in case of a first lamp not functioning,the emitter-base voltage of the transistor is sufficient to render thistransistor conducting and'thereby ignite the auxiliary lamp through thethyristor.

An advantage of this circuit arrangement is that when-due to the failureof one of the main lamps-the voltage across the warning lamp and thethyristor is closed so that the warning lamp lights up. The fault isthen signaled.

A circuit arrangement according to the invention might be used, forexample, in a stationary signaling device or for the lighting of avehicle.

in a special embodiment of the circuit arrangement according to theinvention wherein the first lamp and the second lamp are motorcar lamps,these two lamps are motorcar stop lamps.

An advantage of this special embodiment is that a motorcar driver istimely informed of a fault in the brake signaling system. In a number ofcases this may lead to the prevention of serious traffic accidents.

It is feasible that a switch is incorporated in the circuit which switchis arranged in series with the main lamps as well as with the auxiliarylamp. In that case signaling can only take place if also the voltage onthe bridge including the main lamps is present.

In a further embodiment of the circuit arrangement wherein a switch isprovided between one of the input terminals and the electric bridge, oneend of the series arrangement of the auxiliary lamp and the thyristor isconnected to a point between the switch and the said input terminal Anadvantage of the latter embodiment is that a failure possibly signaledduring the voltage present on the bridge also remains indicated by aburning auxiliary warning lamp after the electric bridge has beenswitched off. In fact, if during operation one of the main lamps is outof order, this will lead to the thyristor arranged in series with thewarning lamp becoming conducting. As a result this lamp lights up.However, if the switch is opened, all main lamps which may still beoperating will be extinguished, but the auxiliary lamp continues tooperate because the current flowing through the thyristor is onlyinterrupted when this current drops below the holding value. The circuitarrangement is proportioned in such a manner that the current flowingthrough the warning lamp is greater than this holding current value andin that case the auxiliary lamp will continue to operate even when theswitch is opened, and hence the signaling of the fault will becontinued.

The two last-mentioned embodiments of the circuit arrangement arepreferably used in combination in a motorcar, the switch being coupledto the brake of the car.

An advantage thereof is that the warning lamp lights up when a fault isrevealed in one of the stop lights during a braking procedure, whichwarning lamp continues to operate also when the driver has released thebrake. In such a system attention is thus drawn for a longer period tothe presence of a fault in one of the vital parts of the signalingsystem of his vehicle.

It is possible to guard each group of two parallel arranged lamps bymeans of an arrangement according to the invention in a vehicle of, forexample, in a system for guarding a panel of signaling lamps.

In a further advantageous embodiment of the circuit arrangement, whereinmore than one group of parallel-arranged lamps is present, all thesegroups of lamps are included in bIidge circuits which are substantiallythe same as those for the group of the first and the second lamp andwherein two limbs of all these bridges are common, these two limbs beingprovided with resistors and wherein a diode is present for each group oflamps which diode connects the junctions of the remaining limbs to amain electrode of the transistor in such a manner that a failure of oneout of the total number of lamps is indicated by the ignition of theauxiliary lamp.

An advantage of the latter embodiment is that a great number of groupsof lamps can be guarded with the aid of one warning lamp.

It is evident that in a system according to the invention the warninglamp lights up -not only when one of the main lamps fails, but also whenboth main lamps fail. In fact, when the two lamps do not light up thevoltage drop across the resistor series arranged with these lamps iszero and also in that case the emitter-base voltage is certainlysufficient to render the transistor conducting. In the foregoingdiscussion reference was always made to two parallel. arranged auxiliarylamps. However, it is alternatively feasible that this number is morethan two and that the resistor which is series-arranged with these lampsis proportioned in such a manner that the voltage across this resistoris sufficient to render the said transistor conducting and thus tosignal the fault when only one of the lamps from this group has failed.

BRIEF DESCRIPTION OF THE DRAWING In order that the invention may bereadily carried into effect, a few embodiments thereof will now bedescribed in detail, by way of example, with reference to theaccompanying diagrammatic drawings, in which:

' FIG. 1 shows a circuit diagram of a circuit arrangement according tothe invention;

FIG. 2 shows a further circuit diagram of a circuit arrangementaccording to the invention; and

FIG. 3 shows a third circuit diagram of a circuit arrange ment accordingto theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, the referencenumerals 1 and 2 are connecting terminals which are intended to beconnected to the battery of a motorcar. The reference numerals 3 and 4denote two stop lamps of the motorcar. The terminals 1 is connected toan electric bridge one limb of which is formed by a resistor 5. Afurther limb of this bridge is formed by a resistor 6 which isseries-arranged with the resistor 5, and a subsequent limb of the bridgeis formed by.a resistor 7. The resistor 7 is arranged between the lamps3 and 4 at one end and the connecting terminal 1 at the other end. Thelamps 3 and 4 together constitute a fourth limb of the bridge. Thisbridge is connected through-a switch 8 to the negative input terminal 2of the circuit arrangement. The switch 8 is mechanically coupled to thebrake of the motor car. The negative terminal 2 is connected to theframe of the car. A junction of the resistors and 6 is connected to thebase of a transistor 9. This transistor is of the pnp'type. The emitterof the transistor 9 is connected to a junction between the resistor 7and the lamps 3 and 4. The collector of the transistor 9 is connectedthrough a subsequent resistor 10 and a capacitor 11 to a conductor 14which connects the resistor 6 to the lamps 3 and 4. The conductor 14 isassociated with the electric bridge. The conductor 14 is connectedthrough the switch 8 to the terminal 2. A junction betweenthe resistor10 and the capacitor 11 is connected to the control electrode of athyristor 12. An auxiliary lamp 13 is incorporated in series with thisthyristor 12. This lamp is the warning lamp. The series arrangement oflamp 13 and thyristor 12 is connected at one end to a junction betweenthe input terminal 1 and the resistor 7 and at the other end to theconductor 14. One end of a diagonal of the said electric bridge isformed by a junction of the resistors 5 and 7, and a further end of thesame diagonal is formed by the part of the switch 8 facing the bridge.The ends of the other diagonal of the bridge are formed by the junctionof the resistors 5 and 6, and the junction of the resistor 7 and thelamps 3 and 4. The resistors in the circuit of FIG. 1 are proportionedin such a manner that the voltage drop across the resistor 7 is so highthat the emitter-base voltage of the transistor 9 is insufficient torender this transistor conducting when the two lamps 3 and 4 function inthe closed condition of the switch 8. In that case the thyristor 12 willalso be non-conducting and hence the lamp 13 is extinguished. However,if one of the two main lamps 3 or 4 fails, the voltage across resistor 7(as a result of the reduced current flow) will decrease so that theemitter of the transistor 9 receives a more positive potential while thepotential on its base remains the same so that this transistor 9 becomesconducting. As a result the capacitor 11 will be charged through theresistor 7 and the resistor 10. When this capacitor has received a givencharge, the thyristor 12 will be rendered conducting thereby through thecontrol electrode of this thyristor and the lamp 13 will light up. Thelamp 13 is installed, for example, on the dashboard of the motorcar. Dueto the lamp 13 lighting up the motorcar driver sees that there issomething wrong with the stop-light system. In that case he can taketimely steps to correct this fault.

The circuit of FIG. 2 largely corresponds to that of FIG. I. Animportant difference is, however, that the switch 8 is replaced by aswitch 18 which is provided between the input terminal 1 and theresistor 7. Furthermore the lamp 13 is connected to a point 19 which islocated between the input terminal 1 and the above-mentioned switch 18.In the case of FIG. 2 the input terminal 2 is furthermore connected tothe common conductor 14. Corresponding circuit elements in FIGS. 1 and 2have the same reference numerals. In the circuit of FIG. 2 the switch 18is also coupled to the brake of the motorcar. If during a brakingprocedure, there is a fault in one of the lamps 3 or 4, the auxiliarylamp 13 will light up in the same manner as described with reference toFIG. 1. However, when the motorcar driver releases the brake and hencethe switch 18 is opened again, the current circuit of lamp l3 andthyristor 12 will remain closed because the current flowing through thethyristor does not fall below the holding current value. As a result thelamp 13 will continue to operate after braking so that the motorcardriver receives a continuous signal of a fault in the stop-light system.The lamp 13 (in the system of FIG. 2)

will not be extinguished until the current from the battery to thedifferent power consumption systems is interrupted, for example, byturning the ignition key of the vehicle.

The circuit of FIG. 3 includes an extension of the circuit of FIG. 2.Corresponding circuit elements in FIGS. 3 and 2 have the same referencenumerals. FIG. 3 shows again two stoplamps 3 and 4. However, the circuitof FIG. 3 also includes a group of two other lamps, to wit, lamps 30 and40. These are, for example, lamps constituting the main lighting of themotorcar (the headlights). In the 'citcuit of FIG. 3 the warning lamp 13guards both the group of lamps 3, 4 and the group of lamps 30, 40. Newelements in FIG. 3 are the resistor 70 which is arranged in series withthe lamps 30 and 40 and a switch 180. The resistor 70 corresponds to theresistor 7 and the switch corresponds to the switch 18. The switch 180is arranged between the resistor 70 and the junction 19 of the circuitarrangement. In the case of FIG. 3 a diode 20 is provided between theemitter of the transistor 9 and the junction between the resistor 7 andthe lamps 3 and 4. Similarly, a diode 200 is provided between theemitter of the transistor 9 and the junction between the resistor 70 andthe lamps 30 and 40. The diodes 20 and 200 serve to prevent current inthe stop-light system 3,4 from flowing over to the system of themotorcar head lamps 30, 40 and also serve to prevent an inverted flow ofcurrent. If, in the switched-on condition of the switch 18, a faultoccurs in one of the lamps 3 or 4 (orin both lamps) the transistor 9will become conducting in the manner already described with reference toFIG. 2, and hence the thyristor 12 will become conducting so that thelamp 13 lights up. Since the lamp 13 is again connected to a point 19located between the input terminal 1 and the switch 18 the fault canremain signalized by the operating lamp 13 even when this switch isreopened. In the closed condition of the switch 180 a possible fault inthe system of the lamps 30 and 40 can be passed on through the resistor70 to the transistor 9, namely because in case of failure of one of thelamps 30 or 40 the potential difference across this resistor 70 issmaller than when both of the lamps 30 and 40 operate satisfactorily. Ifone of the lamps 30 or 40 is out of order, the emitter-base voltage ofthe transistor 9 is sufi'icient to render this transistor conductingand, in the same manner as described with reference to the othercircuit, the capacitor 11 is charged and hence thyristor 12 is renderedconducting so that the lamp 13 lights up. Also in the case of the lamps30 and 40 a possible fault of the lamps 30 or 40 continues to besignaled even after the switch 180 is reopened.

The circuit arrangements described provide a simple and efficient meansfor signaling the failure of one or more lamps of the motorcar.

What is claimed is:

l. A direct current supply circuit for a first lamp comprising anauxiliary lamp for signaling a failure of the first lamp, a pair ofinput terminals adapted for connection to a source of DC current, meansconnecting one input terminal to one end of a diagonal of an electricbridge circuit and the other input terminal to the other end of saidbridge diagonal, said bridge including a resistor in three legs of thebridge and the fourth leg of the bridge including at least the firstlamp, means connecting the ends of the other bridge diagonal to a mainelectrode and to the base of a transistor, respectively, meansconnecting the other main electrode of the transistor through acapacitor to an input terminal, means connecting a junction between saidtransistor other main electrode and the capacitor to the controlelectrode of a thyristor, means connecting the auxiliary lamp and thethyristor in series across the input terminals, said bridge resistorsbeing chosen so that with a voltage present across the input terminalsand with said first lamp not functioning, the transistor base-emitterjunction is forward biased so as to render the transistor conducting andthereby trigger on the thyristor to ignite the auxiliary lamp throughthe thyristor.

2. A circuit as claimed in claim 1, further comprising a second lampconnected in parallel with said first lamp and wherein the first lampand the second lamp are motorcar lamps, said bridge resistors beingchosen so that a failure of either of said first and second lamps willforward bias the transistor base-emitter junction to provide saidtrigger action.

3. A circuit as claimed in claim 1 further comprising a switch connectedbetween one of the input terminals and the electric bridge,characterized in that one end of the series arrangement of the auxiliarylamp and the thyristor is connected to a point between the switch andthe said input terminal so that said series arrangement is connected tothe input terminals even in the open condition of the switch.

4. A circuit as claimed in claim 2 provided in a motorcar and furthercomprising a switch coupled to the brake of the motorcar and seriallyconnected with the bridge circuit across said input terminals.

5. A circuit as claimed in claim 1 further comprising a second lamp anda second resistor connected in series therewith across the inputtenninals to form a second bridge circuit along with the two series legsof the first bridge circuit that include the resistors, first and seconddiodes, means conmeeting the first and second diodes between saidtransistor main electrode and the associated end of the bridge diagonaland the junction ofsaid second lamp and the second resistor,respectively, so that a failure of any one of the main lamps willtrigger the thyristor and thereby ignite the auxiliary lamp.

6. A circuit as claimed in claim 5 further comprising a third lampconnected in parallel with the first lamp and a fourth lamp connected inparallel with the second lamp whereby a failure of any one of the mainlamps will trigger the thyristor and thereby ignite the auxiliary lamp.

7. A DC supply and indicating system for a first lamp comprising, a pairof input terminals adapted for connection to a source of DC current, anauxiliary lamp for signalling a failure in said first lamp, a thyristorconnected in series with said auxiliary lamp directly across the inputterminals, a first resistor connected in a first series circuit withsaid first lamp across said input terminals, a transistor and animpedance element connected in a second series circuit with said firstresistor across the input terminals, means coupled to said inputterminals and to the transistor for biasing the transistor into thecut-off state, means for coupling the voltage derived across saidimpedance element to the thyristor control electrode for controlling theignition thereof, said derived voltage being of sufficient magnitude totrigger the thyristor into conduction upon a failure of said first lamp,and a switch connected in series with at least one of said first andsecond series circuits across the input terminals.

8. A system as claimed in claim 7 further comprising a second lampconnected in parallel with the first lamp, and wherein said biasingmeans is arranged to allow a substantial current to flow in saidtransistor upon the failure of either one of said first and second lampsthereby to derive said trigger voltage across said impedance element.

9. A system as claimed in claim 8 wherein said impedance elementcomprises a capacitor.

10. A system as claimed in claim 8 further comprising a first diodeconnected in series with said first resistorand said transistor, thirdand fourth lamps connected in parallel, a second resistor and a seconddiode, means connecting said second resistor and said parallel-connectedthird and fourth lamps in a third series circuit across the inputterminals, and means connecting said second diode in series with saidsecond resistor and said transistor.

1 1. A system as claimed in claim 7 for use in a motorcar and furthercomprising means for coupling said switch to the motorcar brakemechanism.

1. A direct current supply circuit for a first lamp comprising anauxiliary lamp for signaling a failure of the first lamp, a pair ofinput terminals adapted for connection to a source of DC current, meansconnecting one input terminal to one end of a diagonal of an electricbridge circuit and the other input terminal to the other end of saidbridge diagonal, said bridge including a resistor in three legs of thebridge and the fourth leg of the bridge including at least the firstlamp, means connecting the ends of the other bridge diagonal to a mainelectrode and to the base of a transistor, respectively, meansconnecting the other main electrode of the transistor through acapacitor to an input terminal, means connecting a junction between saidtransistor other main electrode and the capacitor to the controlelectrode of a thyristor, means connecting the auxiliary lamp and thethyristor in series across the input terminals, said bridge resistorsbeing chosen so that with a voltage present across the input terminalsand with said first lamp not functioning, the transistor base-emitterjunction is forward biased so as to render the transistor conducting andthereby trigger on the thyristor to ignite the auxiliary lamp throughthe thyristor.
 2. A circuit as claimed in claim 1, further comprising asecond lamp connected in parallel with said first lamp and wherein thefirst lamp and the second lamp are motorcar lamps, said bridge resistorsbeing chosen so that a failure of either of said first and second lampswill forward bias the transistor base-emitter junction to provide saidtrigger action.
 3. A circuit as claimed in claim 1 further comprising aswitch connected between one of the input terminals and the electricbridge, characterized in that one end of the series arrangement of theauxiliary lamp and the thyristor is connected to a point between theswitch and the said input terminal so that said series arrangement isconnected to the input terminals even in the open condition of theswitch.
 4. A circuit as claimed in claim 2 provided in a motorcar andfurther comprising a switch coupled to the brake of the motorcar andserially connected with the bridge circuit across said input terminals.5. A circuit as claimed in claim 1 further comprising a second lamp anda second resistor connected in series therewith across the inputterminals to form a second bridge circuit along with the two series legsof the first bridge circuit that include the resistors, first and seconddiodes, means connecting the first and second diodes between saidtransistor main electrode and the associated end of the bridge diagonaland the junction of said second lamp and the second resistor,respectively, so that a failure of any one of the main lamps willtrigger the thyristor and thereby ignite the auxiliary lamp.
 6. Acircuit as claimed in claim 5 further comprising a third lamp connectedin parallel with the first lamp and a fourth lamp connected in parallelwith the second lamp whereby a failure of any one of the main lamps willtrigger the thyristor and thereby ignite the auxiliary lamp.
 7. A DCsupply and indicating system for a first lamp comprising, a pair ofinput terminals adapted for connection to a source of DC current, anauxiliary lamp for signalling a failure in said first lamp, a thyristorconnected in series with said auxiliary lamp directly across the inputterminals, a first resistor connected in a first series circuit withsaid first lamp across said input terminals, a transistor and animpedance element connected in a second series circuit with said firstresistor across the input terminals, means coupled to said inputterminals and to the transistor for biasing the transistor into thecut-off state, means for coupling the voltage derived across saidimpedance element to the thyristor control electrode for controlling theignition thereof, said derived voltage being of sufficient magnitude totrigger the thyristor into conduction upon a failure of said first lamp,and a switch connected in series with at least one of said first andsecond series circuits across the input terminals.
 8. A system asclaimed in claim 7 further comprising a second lamp connected inparallel with the first lamp, and wherein said biasing means is arrangedto allow a substantial current to flow in said transistor upon thefailure of either one of said first and second lamps thereby to derivesaid trigger voltage across said impedance element.
 9. A system asclaimed in claim 8 wherein said impedance element comprises a capacitor.10. A system as claimed in claim 8 further comprising a first diodeconnected in series with said first resistor and said transistor, thirdand fourth lamps connected in parallel, a second resistor and a seconddiode, means connecting said second resistor and said parallel-connectedthird and fourth lamps in a third seriEs circuit across the inputterminals, and means connecting said second diode in series with saidsecond resistor and said transistor.
 11. A system as claimed in claim 7for use in a motorcar and further comprising means for coupling saidswitch to the motorcar brake mechanism.